In a CMOS image sensor, a pixel area is reduced according to an increase in the number of pixels. When pixel size is reduced, the number of saturated electrons of the pixels cannot be sufficiently secured. Therefore, the pixel area is reduced and the number of saturated electrons of the pixels is increased by adopting a four-pixel one-cell structure to cause four pixels to share a reset transistor and an amplifier transistor.
For example, Japanese Patent Application Laid-Open No. 2008-227253 discloses a method of providing, on a front surface side of a semiconductor substrate, a plurality of photoelectric conversion elements formed in a two-dimensional array shape, CCD-type signal readout means for reading out detection signals of the photoelectric conversion elements, and MOS-type signal readout means for reading out detection signals of the photoelectric conversion elements in a back-illuminated solid-state imaging device.